Lugia and articuno
almost all of the water type Pokemon can learn and use waterfall
Most water Pokemon will learn waterfall i believe. For certain if you have PIPLUP, TENATACOOL, or TENTACRUEL, it will learn Waterfall. Hope I Helped!
Most water type Pokemon can learn the move Waterfall.
all pure water types can learn waterfall ( like panpour and other water types
The only Pokemon that learn Waterfall by leveling up are Goldeen and Seaking, but most Water types may learn it by HM07, which can be found in Ice Path.
Very badly worded question, I'd interpret it as "Why can't any of my Pokemon learn waterfall?". To answer the question, the most likely reason is that you don't have any water type pokemon. The great majority of water types are able to learn Waterfall through the HM obtained ingame.
a strong water Pokemon (ferligater blastoise golduck etc)
Most water types can like sharpedo.
You can find it at Route 18. Just fly to Nuvema Town and go to route 1, past the patch of grass, and turn left and when you get to the water make sure you have surf then swim across and eventually you will get to Route 18 if you keep following the path and HM Waterfall will be somewhere around there.
I sure know about empoleon (prinplup and piplup too) that he can learn it, and i think every water type can learn.
By itself:only goldeen,seaking With Tm:Mostly any water or dragon pkmn
Only Goldeen and its evolution Seaking learn Waterfall naturally. There are nearly 100 pokeman that learn Waterfall through HM. Rather than list them, Just use this site: http://www.serebii.net/attackdex-dp/waterfall.shtml